Analysis of the electronic structure and local coordination of an element is an important aspect in the study of the chemical and physical properties of materials. This is particularly relevant at ...the nanoscale where new phases of matter may emerge below a critical size. X-ray emission spectroscopy (XES) at synchrotron radiation sources and free electron lasers has enriched the field of X-ray spectroscopy. The spectroscopic techniques derived from the combination of X-ray absorption and emission spectroscopy (XAS-XES), such as resonant inelastic X-ray scattering (RIXS) and high energy resolution fluorescence detected (HERFD) XAS, are an ideal tool for the study of nanomaterials. New installations and beamline upgrades now often include wavelength dispersive instruments for the analysis of the emitted X-rays. With the growing use of XAS-XES, scientists are learning about the possibilities and pitfalls. We discuss some experimental aspects, assess the feasibility of measuring weak fluorescence lines in dilute, radiation sensitive samples, and present new experimental approaches for studying magnetic properties of colloidal nanoparticles directly in the liquid phase.
The combination of X-ray absorption with X-ray emission spectroscopy requires careful consideration of the experimental protocol. The article discusses general aspects with examples for bio-catalysis and colloidal magnetic nanoparticles.
We report on the dielectric and electrocaloric properties of Ba1−yCayTi1−xHfxO3 for compositions 0.12 < x < 0.18 and y = 0.06, as well as x = 0.15 and 0 < y < 0.15, synthesized by the conventional ...solid-state reaction method. The addition of Hf/Ca broadens the ferroelectric-paraelectric phase transition while moving it toward room temperature. Two interferroelectric transitions are seen to converge, together with the ferroelectric–paraelectric phase transition, at ∼335 K for 0.12 < xc < 0.135 and y = 0.06. Consistent with the dielectric properties, the electrocaloric effect maximizes closer to room temperature with increasing Hf/Ca substitutions, which promote larger temperature spans. The electrocaloric responsivity gradually decreases from 0.2 to 0.1 K mm kV−1 with the addition of Hf/Ca. A homemade quasi-adiabatic calorimeter is employed to measure “directly” the electrocaloric data, which are also calculated from polarization-versus-electric-field cycles using “indirect” standard procedures. The comparison between measured and calculated values highlights the importance of having access to direct methods for a reliable determination of the electrocaloric effect.
Landslides are common features in the vicinity of volcanic islands. In this contribution, we investigate landslides emplacement and dynamics around the volcanic island of Martinique based on the ...first scientific drilling of such deposits. The evolution of the active Montagne Pelée volcano on this island has been marked by three major flank‐collapses that removed much of the western flank of the volcano. Subaerial collapse volumes vary from 2 to 25 km3 and debris avalanches flowed into the Grenada Basin. High‐resolution seismic data (AGUADOMAR‐1999, CARAVAL‐2002, and GWADASEIS‐2009) is combined with new drill cores that penetrate up to 430 m through the three submarine landslide deposits previously associated to the aerial flank‐collapses (Site U1399, Site U1400, Site U1401, IODP Expedition 340, Joides Resolution, March–April 2012). This combined geophysical and core data provide an improved understanding of landslide processes offshore a volcanic island. The integrated analysis shows a large submarine landslide deposit, without debris avalanche deposits coming from the volcano, comprising up to 300 km3 of remobilized seafloor sediment that extends for 70 km away from the coast and covers an area of 2100 km2. Our new data suggest that the aerial debris avalanche deposit enter the sea but stop at the base of submarine flank. We propose a new model dealing with seafloor sediment failures and landslide propagation mechanisms, triggered by volcanic flank‐collapse events affecting Montagne Pelée volcano. Newly recognized landslide deposits occur deeper in the stratigraphy, suggesting the recurrence of large‐scale mass‐wasting processes offshore the island and thus, the necessity to better assess the associated tsunami hazards in the region.
Key Points:
First drilling into submarine landslide deposits offshore volcanic island
Large (300 km3) submarine landslide deposit offshore Martinique comprises mainly deformed seafloor sediment, in a single frontally emergent morphology
The determination of the local orientation and magnitude of the magnetization in spin textures plays a pivotal role in understanding and harnessing magnetic properties for technological applications. ...Here, we show that by employing the polarization dependence of resonant inelastic X-ray scattering (RIXS), we can directly probe the spin ordering with chemical and site selectivity. Applied on the prototypical ferrimagnetic mixed-valence system, magnetite (Fe3+AFe3+,Fe2+BO4), we can distinguish spin-flip excitations at the A and B antiferromagnetically coupled Fe3+ sublattices and quantify the exchange field. Furthermore, it is possible to determine the orbital contribution to the magnetic moment from detailed angular dependence measurements. RIXS dichroism measurements performed at spin-flip excitations with nanometer spatial resolution will offer a powerful mapping contrast suitable for the characterization of magnetic ordering at interfaces and engineered spin textures.
In the Alboran Sea, the Mediterranean coastline of Morocco is exposed to tsunami hazard. The average regional seismicity (≈ 6.6 Mw) may be the direct cause of this phenomenon and may enhance the ...possibility of occurrence of submarine landslides, a potential indirect source of tsunami. Recent events in the Indian and Pacific Oceans have demonstrated that tsunamis are difficult to predict and devastating. Thus, they constitute a latent threat to the Moroccan coastal population. The present study gathers the first reflections on the exposure of the stakes of the Moroccan northern coastline to contribute to an integrated and dynamic approach of the Mediterranean coastal risks. It analyses the tsunami hazard in the geological context of the Alboran Sea. It also highlights the characteristics of the human occupation of the Moroccan coasts. The Tetouan tourist coastline, the Al Hoceima agricultural plain and the Nador lagoon appear to be the territories most exposed to a potential tsunami. The variety of urban, tourist, agricultural and environmental issues results in an exhaustive diagnosis of the exposure of Morocco’s Mediterranean coastline.
The Alboran Basin may be subject to tsunami hazards. If such an event were to occur, it is expected that the urbanised and densely populated areas of northern Moroccan coastline would be affected. ...Precise inundation hazard maps are needed for tsunami risk management in this region. In this article, we argue that the diversity of hazard mapping methods ensures the robustness of the scientific knowledge about the exposure of a territory. Hence, the main objective of this study is to analyse the exposure of the plain of Martil (north of Morocco), by using four hazard mapping methods to create inundation maps for two scenarios of tsunamis generated by extreme submarine mass failure (SMF) in the Alboran Sea, of 0.9 km3 and 3.8 km3 respectively. A digital terrain model of the plain was used to explore four methods of inundation mapping. The static method identified 4.32 km2 and 19.83 km2 of flooded areas for each scenario using water height values as inundation thresholds. The hybrid and the volumetric methods use the volume of water to determine the inundation extent. For the first scenario, 3.51 km2 of the plain were inundated using the hybrid method, and 20.11 km2 for the second scenario. The results of the volumetric methods are 2.32 km2 and 7.82 km2 respectively for the first and second scenario. Finally, the fourth method relies on numerical hydrodynamic modelling of tsunami inundation (Freshkiss3d® code). With this method, 4.55 km2 of the plain were flooded in the first scenario, and 24.12 km2 for the second. The comparison of the results highlights that the most sensitive areas to tsunami inundation are the lowest topographic ones, being the beaches and the wadis floodplains. This result raises questions on the current coastal development and the preparedness of its population, thus calling for more attention to engage on tsunami risk management related questions.
•Comparison of four hazard mapping methods for two extreme tsunami events scenarios.•Evaluation of the degree of exposure of the touristic plain of Martil.•Discuss the regional development strategies with potential tsunami impacts.•Provide a flexible toolset for decision-makers in tsunami risk management.
K-fluorescence X-ray emission spectroscopy (XES) is receiving growing interest in all fields of natural sciences to investigate the local spin. The spin sensitivity in Kβ (Kα) XES stems from the ...exchange interaction between the unpaired 3p (2p) and the 3d electrons, which is greater for Kβ than for Kα. We present a thorough investigation of a large number of iron-bearing compounds. The experimental spectra were analyzed in terms of commonly used quantitative parameters (Kβ1,3-first moment, Kα1-full width at half-maximum, and integrated absolute difference −IAD−), and we carefully examined the difference spectra. Multiplet calculations were also performed to elucidate the underlying mechanisms that lead to the chemical sensitivity. Our results confirm a strong influence of covalency on both Kβ and Kα lines. We establish a reliable spin sensitivity of Kβ XES as it is dominated by the exchange interaction, whose variations can be quantified by either Kβ1,3-first moment or Kβ-IAD and result in a systematic difference signal line shape. We find an exception in the Kβ XES of Fe3+ and Fe2+ in water solution, where a new difference spectrum is identified that cannot be reproduced by scaling the exchange integrals. We explain this by strong differences in orbital mixing between the valence orbitals. This result calls for caution in the interpretation of Kβ XES spectral changes as due to spin variations without a careful analysis of the line shape. For Kα XES, the smaller exchange interaction and the influence of other electron–electron interactions make it difficult to extract a quantity that directly relates to the spin.
The products of eruptive and mass-wasting processes that built island arc volcanoes are better preserved in marine deposits than on land. Holes U1397A and U1399A drilled during IODP Expedition 340 ...provide a 1.5 Ma record of the volcanic history of Martinique.
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C dating and δ
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O patterns are used to reconstitute the chronostratigraphy of tephra, volcaniclastic turbidites, and mass-wasting events (traced by debris avalanches, debrites, and duplication and deformation of pre-existing sediments), leading to a new volcanic history of Montagne Pelée and Pitons du Carbet volcanoes. The top 50 m of core U1397A provides a continuous high-resolution sedimentation record over the last ∼130 ka. The sedimentation record deeper than 50 m in core U1397A and in the whole core U1399A is discontinuous because of the numerous sliding and deformation events triggered by debris avalanches related to flank collapses. Three successive activity periods are identified since ∼190 ka: the “Old Pelée” until 50 ka, the “Grand Rivière” (50–20 ka), and the “Recent Pelée” (20 ka—present day). The first two periods have the highest volcanic deposition rates offshore but very little outcrop on land. The whole magmatic activity of Mt Pelée comprises silicic andesites, but mafic andesites were also emitted during the whole “Grand Rivière.” At ∼115 ka, a major flank collapse (“Le Prêcheur”) produced a debris avalanche and submarine landslide that affected sea floor sediments by erosion and deformation up to ∼70 km from the shore. The Pitons du Carbet volcano was active from 1.2 Ma to 260 ka with numerous large flank collapses at a mean rate of 1 event every 100 ka. The average deposition rate of tephra fall offshore is much less than that at Mt Pelée. Our data show that correlations between the timing of large landslides or emission of mafic magmas and rapid sea level rise or lowstands suggested by previous studies are not systematic. The reconstituted chronostratigraphy of cores U1397A and U1399A provides the framework necessary for further studies of the magma petrology and production rates and timing of the mechanisms triggering flank collapses and related submarine landslides of Mt Pelée and Pitons du Carbet
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To improve understanding of evolution of submarine canyons, a three‐dimensional slope stability model is applied to Bourcart Canyon in the western Gulf of Lions in the Mediterranean Sea. The model ...builds on previous work by Z. Chen and others, and it uses the upper bound theorem of plasticity to calculate the factor of safety of a kinematically admissible failing mass. Examples of three‐dimensional failure surfaces documented in the literature were used to test the model formulation. Model application to Bourcart Canyon employed the results of detailed stratigraphic analyses on the basis of data acquired by swath bathymetry, subbottom profiling, high‐resolution seismic reflection surveys, and piston coring. The sediment layers were also characterized using in situ geotechnical measurements and laboratory tests. The effects of three loading scenarios were analyzed: (1) earthquake shaking, (2) hemipelagic sedimentation, and (3) axial incision. These three mechanisms influenced the predicted volumes and shapes of slope failures along the flanks of Bourcart Canyon, and comparison of these predictions with failure geometries inferred from seafloor morphology showed that mass failures could account for the observed morphology along the canyon walls as well as a mechanism of canyon widening.
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